Apparatus for measuring ultra high frequency field distributions



y 1, 1951 s. SENSIPER 2,551,398

APPARATUS FOR MEASURING ULTRA HIGH FREQUENCY FIELD DISTRIBUTIONS FiledMay 17, 1946 IlllHlIlI ATTOR N EY Patented May 1, 1951:APPARATUSrFQKMEASURING ULTRA. IG FREQUENCY FIELD DISTRIBUTIONS Samuel-SensipenGarden City, N. Y., assignor, to

i'TheSperry Corporation, a corporation of Delaware -.-ApplicationMay,17, 1946', SeriaLNo, 670,391

2 Claims. 1

This invention relates to ultra-high-frequency electrical apparatus andmore particularly to improvements in. standing wave detectors usingtravelling probes.

The conventional standingwave detector consists of a section of coaxialline with a slot running along the outer conductor to permit'loosecoupling of a radio-frequency voltmeter probe to the line. Such aslotted sectionis used to determine the ratio of voltage amplitudes, atvoltage nodes and anti-nodes of standing waves along the line, and todetermine the relative positions of these nodes and anti-nodes. Fromsuch data it ispossible to. determine'the resistive and reactive natureof a load coupled to the line. Considerable caremust be taken inthedesign of such standing wave detectors that the probe shall respond onlyto the standing Wave inthe coaxial line. Any radiation leakingoutthrough .the. slotted section whichmight. later. be reflected back tothe probe and picked up by it, makes standing wave measurementshighlyinaccurate. Also, it is quite possible for electromagnetic energyfrom some other undesirable source to. enter the slotted sectionthrough'the slot and thereby cause a false reading. Itis also possiblefor the pickup probe itself to act as a small antenna and to radiatesome of the electromagnetic energy by which it is excited. This radiatedenergy may be reflected back to the probe or otherwiseicause furtherinaccuracies in. the measurement.

The principal object of, this invention is toprovideanultra-high-frequency energy absorber in the immediate neighborhood ofa pickup probe or coupling device or other member which communicateswith the interior of an enclosed-conductor type of transmission systemor standingwave enclosure,,so that undesirable'electromagnetic energyWill be prevented frominterfering with the desired fields of such asystem or enclosure.

Another object of the present invention is to provide a travelling probethat is unaffected by undesirable outside sources of electromagneticenergy.

.A furtherv object -of the present invention is to provide a travellingprobe having an energy trap .which prevents undesired energy fromaffecting the probe, such an energy trap .having little .or no frequencysensitivity.

Briefly, the present invention provides the usual slotted coaxial lineor wave guide with a travelling probe whose carriage has a large bear-.ing surfaceand. slides ,along, the slotted coaxial line or wave guidesection. The novel feature in this travelling probelies in the use of. ablock .or blocks of electromagnetic-energy-absorbing material insertedin the bearing surface of the probe carriage in the neighborhood of theprobe.

An example of such material that has been found to be very efiective isthat sold under the trade name fPolyiron. Thismaterial comprises sm'allparticles of iron,. or powdered iron, held together by a binderof'dielectricmaterial such asBakelite, and is wrell known in the radioart foruse as magnetic cores in intermediate frequencyand radiofrequencytransformers. It is described in Iron Core Intermediate FrequencyTransformers by Alfred 'Crossley, on page 298 orthe-"November .1933issue of'Electronics Magazine, published by 'McGraW=I-Iilt Co., NewYork;-- N.-'Y. By placing such energy-absorbing material at the bearingsurface-of the travelling probe, anenergy sink of microwave. energy isprovided. This energy sink absorbs both the incident energy from outsidesources as well as any energy whichthe pickup probe or the'slot may tendto radiate when acting as an antenna. It' can readily be seen,therefore, that by inserting suitable energy-absorbing units, suchas-Polyiron membersdn the immediate vicinity of the pickup-probe outsideof the outer conductor of the slotted coaxial line section, the responseof the pickupprobe is confined to the energy represented by the standingwave which'exists in thecoaxial line, and spurious response isminimized.

The invention in another-of its aspects relates to novel features of the'instrumentalities-described herein-for achieving the principal objectsof the invention and to novel principles employed in thoseinstrumentalities, whether or not these features and principles are usedfor the said principal'objects or inthe said field.

A further object of the inventionisto provide improved apparatus andinstrumentalities embodying novel features and principles, adapted forusein realizing the above objects andalso adapted for use in otherfields.

.Othenobjects and advantages will become apparent from thespec'ificaticmtaken in connection with, the accompanying drawingwherein:

Fig. l is a side elevation viewpartlyin crosssection of acoaxial-line-typeoi standing wave detector incorporating a preferredembodiment of this invention;

. Fig, 2,is..an end elevation view partly, in crosssection ofthestanding .wave detector-showmin Fig.1, .viewed'from; the rightsidethereof; and

,Fig. ;3..is a fragmentary and..elevation, view, partially incross-section, of a standing wave detector of the wave guide typeincorporating the present invention.

Reference to Fig. 1, which is a side elevation view of acoaxial-line-type standing-wave detector, shows a slotted coaxial linesection it which is terminated at each end in a standard coaxial linecoupling member and I2. The center conductor l3, of the line issupported by conventional T-stub supports l4 and i5 at each end of theslotted line section H]. Probe carriage i6 is supported by a bearingsurface 24 on slotted line section l0 and is capable of being moved intranslation by rotation of knob ll. Such translatory motion may becalibrated and indicated by the aid of scale l8 engraved on the outerfront face IQ of slotted section l5. A small vernier scale 26 used foraccurate reading is provided on the face of probe carriage l5. Rigidlymounted on top of probe carriage i6 is a wave guide coupling section 2|which supports a tuning unit 22 and a radiofrequency detector unit 23.

Fig. 2, which is an end elevation view of the standing wave detectorshown in Fig. 1 partly in cross section, shows the details of probecarriage l6, wave guide coupling unit 2|, tuning unit 22 and R. F.detector unit 23. As can best be seen in this figure, slotted linesection H) has a large flat upper bearing surface 24 through which iscut longitudinal slot 25. Inserted in the base of the adjacent bearingsurface 26 of probe carriage I6 is a slab ofelectromagnetic--energyabsorbing material 21. This slab 2'5 runs thelength of probe carriage It. A hole 28 is provided in the slab 2'! topermit a sleeve-like portion of probe carriage Hi to project downwardlyinto slot 25. An opening 28 in the portion 16 allows the probe 29 topass therethrough to communicate with the interior of coaxial linesection IS. A dielectric supporting bushing 35 is used to maintain probe29 in a relatively coaxial probe within sleeve-like portion 10 ofrelation carriage Hi. The probe element 29 and sleeve-like portion 10thus cooperate as a coaxial line probe unit.

Probe 29 extends through probe carriage l5, 1-,

across a wave guide coupling unit 2|, and along the length ofcylindrical turning unit 22. Wave guide coupling unit 2| is excited bythe section of the probe 29 which passes through it. The electromagneticfield oscillations which are set up in the wave guide coupling unit 2|are rectified by radio-frequency detector unit 23. This radio frequencydetector unit 23 is of conventional type having a crystal detectorcartridge 3| supported across the wave guide coupling unit 2|. crystaldetector cartridge 3| comprises a metal base 32 with metal cap 33, aninsulator body 34, and a probe or terminal pin 35. Knurled metal cap 36is provided for holding crystal detector cartridge 3| in place and forpermitting its easy replacement.

The metal probe or terminal pin 35 is insulatingly supported in thecenter of detector unit .23 and is electrically connected to center pin87 of the coaxial output connection 38. This output connection 38 hasits outer conductor 35 threaded in order to make good mechanical andelectrical connection to an output cable or any other output connector.

Probe tuning unit 22 is provided to permit efficient coupling betweenprobe 29 and radiofrequency detector unit 23. Member 45 is provided witha bore to receive probe 29, and they coextend from dielectric bushing 35to the upper end of cylindrical tuning unit 22. Tuning unit This 22consists of a metal cylinder 4| which is thread edly coupled to waveguide coupling unit 2| by a metal bushing 42 which is rigidly fastenedto the upper wall 43 of wave guide coupling unit 2|. and within whichcylinder 4| is threaded. A metal plug 44 is fixed in the open end ofcylinder 4| and supports coaxial member and probe 29 at their upperends, so as to maintain their coaxial position inside cylinder 4|. Thevertical position of probe 29 can be manually adjusted at the upper end45 of coaxial member 40 by sliding it inside and along member 40. A setscrew 46, mounted in metal plug 44, engages probe 29 through an openingin member 40 to maintain the vertical adjustment of probe 29. The metalcap 41, which is threadedly engaged to metal plug 44, covers the exposedend of probe 29 projecting upwardly from member 40 where they protrudethrough metal plug 44.

Tuning ring 56 is used to vary the position of a shorting plug 5| insidethe tuning unit 22. Shorting plug 5| short-circuits conductor 45 tocylinder 4|. As tuning ring is rotated, it moves in translation alongcylindrical tube 4| by virtue of the external threads 52 on the outersurface of cylinder 4|. This translatory motion along the axis ofcylinder 4| is transferred to shorting plug 5| by means of pins 53 whichpass through longitudinal slots 54 in the wall of cylinder 4i and rotatefreely within ring 59. A plurality of metal fingers 55 extend from theshorting plug 5| along the inside wall of cylinder 4| and along theouter wall of coaxial member 4|] to provide good electrical contactbetween these members and shorting plug 5 I.

In operation, the slotted coaxial line section Ii! is connected intandem in the transmission system whose standing wave ratio it isdesired to measure. Since the slotted coaxial section if] is terminatedin standard coupling members H and I2, little difiiculty is experiencedin inserting such a line section H3 in the system. Probe-- carriage I6is moved in translation along slotted coaxial section H3 by rotation ofknob ii. If the terminal 31, 35 of radio frequency detector unit 23 isconnected to a suitable indicating unit, say a milliameter, readingsproportional to the amplitude of the standing wave at various positionsalong the slotted section 5 will be indicated. By rotating metal tuningring the wave guide coupling unit 2| can be tuned to give maximumcoupling from pickup probe 29 to radio frequency detector unit 23. Ifgreater coupling between the coaxial line section I6 and the pickupprobe 29 is desired, the probe 29 may be made to protrude further intothe coaxial member 40. Such adjustment may be maintained by tighteningset screw 46 which looks the probe 29 in its vertical position withincoaxial member 4|].

By virtue of the presence of electromagneticenergy-absorbing slab 2'!through which the probe 29 passes, energy from external sources whichfinds its way down the small crack between the upper bearing surface 24of the coaxial line section I5 and the adjacent bearing surface 26 ofthe probe-carriage i5 is prevented from reaching probe 29. Instead it isabsorbed by the slab 21. In like manner, should the probe 29 act as aradiator of the energy which it picks up in the coaxial line, suchenergy could not be reflected back to the probe 29 because of itsabsorption by surrounding slab 27. This absorption of undesired incidentenergy as well as the absorption of any energy which the probe 29radiates is in no way frequency sensitive, if the attenuationcharacteristic of the energy-absorbing material with respect tofrequency is approximately constant over the range which the device isoperable. Thus, should the undesired incident energy be appreciablyremoved in frequency from the frequency of the energy being measured inthe device, the absorbing slab 21 will still successfully prevent thisundesired energy from reaching the pickup probe 29, thus preventinginaccurate readings.

Although in the embodiment shown of the present invention, the pickupdevice is mounted on a slotted coaxial line, it will be obvious to oneversed in this art that the invention is equally advantageous in otherenclosed-conductor types of transmission systems, such as of the waveguide type.

An example of such a wave guide type of standing wave detectorincorporating the present invention is shown in Fig. 3. slotted sectionof rectangular guide 60 is used as the energy-conducting member in placeof the coaxial line section of Fig. 1. As in the embodiment shown inFig. 1, energy-absorbing member 21 is provided adjacent to probe 29 withan opening 28 to permit probe 29 to communicate with the interior ofwave guide member 60. This energy-absorbing member 21 prevents undesiredenergy from external sources from reaching probe 29. It further preventsenergy which might be radiated by probe 29 from later being reflectedback to the probe 29, thereby causing incorrect readings.

It should be pointed out that the invention is not limited in any way tothe use of any particular microwave energy-absorbing material, such asPolyiron, or to its specific location herein illustrated, but in itstrue sense includes any manner of providing a microwave energy sink inthe immediate neighborhood of the opening from which or into whichradiation is to be prevented.

It is further desired to point out that, although in its preferredembodiment the invention is used in conjunction with a pickup probe, inits broader aspects it is equally advantageous when used K with anyother type of coupling devices, or with any member (such as a tuning orshorting device) which passes through the outer wall of anultra-high-frequency energy conductor or resonator. Its use in suchdevices is to prevent the radiation of energy which might leak outthrough any openings between such devices and the outer wall of such anultra-high-frequency conductor or resonator, and to prevent the entrythrough such openings of undesired energy from external sources,

What is claimed is:

1. Apparatus for measuring ultra high frequency field distributionscomprising an electromagnetic wave energy conduit having an enclosingwall provided with a longitudinal slot, a

In this device a pair of conductive metal bearing surfaces extendingalong the outside of said wave conduit adjacent each side of said slot,a probe carriage having a pair of correlated bearing surfaces slidablyengaging said first mentioned bearing surfaces for motion of saidcarriage along said slot, a pickup probe unit supported by said carriageand comprising a conductive sleeve integral with said carriage andextending through said slot and spaced from the edges thereof andterminating substantially flush with the inner surface of said wall ofsaid wave conduit, and an inner conductor substantially coaxial withsaid sleeve and extending into said wave conduit beyond said innersurface as the probe element therein, and a block of ultra highfrequency energy absorbing material comprising finely divided particlesof ferromagnetic material suspended in a solid dielectric material, saidblock being disposed between said bearing surfaces on said carriage,surrounding said sleeve and extending substantially the length of saidcarriage adjacent said slot, and in contact substantially throughout itslength with the outside wall of said -wave conduit.

2. Ultra high frequency electromagnetic wave energy apparatus comprisingan electromagnetic wave conduit having an enclosing wall provided with alongitudinal slot, a probe carriage movable along said slot, a probeunit supported by said carriage and comprising a coaxial line having itsouter conductor ending substantially flush with the inner surface ofsaid wall and its inner conductor extending therebeyond into theinterior of said conduit as the probe element therein, and a body ofultra high frequency energy absorbing material comprising finely dividedparticles of ferromagnetic material suspended in a solid dielectricmaterial, said body surrounding said probe unit between said carriageand the outside surface of said wall of said wave conductor, andextending substantially throughout the portion of said carriage adjacentsaid slot.

SAMUEL SENSIPER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,984,526 Given Dec. 18, 19342,293,839 Linder Aug. 25, 1942 2,402,663 Ohl June 25, 1946 2,404,797Hansen July 30, 1946 2,409,640 Moles Oct. 22, 1946 2,412,805 Ford Dec.1'7, 1946 2,439,527 Paulson Apr. 13, 1948 2,443,109 Linder June 8, 19482,454,042 Dettinger Nov. 16, 1948 2,465,719 Fernsler Mar. 29, 1949

